The present invention relates generally to a steering assembly for a work vehicle suitable for use over uneven ground, and more particularly to a steering mechanism for a tractor.
The present invention may be used to advantage on a farm tractor, to which the following description refers purely by way of example.
In farming, wheel-mounted tractors are used for towing mechanical or chemical land processing machinery. The frame, which on recent tractor models comprises the engine block, supports at the front a steering assembly with a rotary T-shaped front shaft. European Patent Application n. EP-A 0.691.258, entitled "Steering mechanism for compact tractors," describes a steering assembly comprising a front axle defined axially by rocking end portions, and a box body connected to the frame by a spherical joint. Each of the rocking end portions carries a direction wheel, and is connected to the box body by a linear actuator by which it is rotated with respect to the axle. The steering assembly also comprises a rod connecting the box body and the frame at the rear wheel end to enable the front axle to oscillate about a horizontal axis; and the rod is connected to the box body by a substantially vertical cylindrical hinge, and to the frame by a spherical joint, so that the rod is mainly subjected to traction. Finally, the steering assembly also comprises a pair of ties, each of which is connected to the frame alongside the spherical joint connecting the box body to the frame and to the respective rocking end portion.
It should be pointed out that the distance between the spherical joint, connecting the axle to the frame, and the axis of the rear wheels is less than the distance between the front and rear wheels; and the ties rotate the axle with respect to the respective spherical joint at each opposed activation of the linear actuators, so that the motion of the direction wheels with respect to the frame is a combination of the rotation of each direction wheel with respect to the corresponding end of the axle, and of the box body with respect to the frame, and provides for maneuvering the vehicle in a very small space.
Such a steering assembly therefore provides for a high degree of maneuverability of the tractor, and for maintaining ground contact of the direction and rear wheels even when traveling over rough ground. On the other hand, however, as the resistance opposed by the terrain to the forward movement of the tractor is transmitted directly to the frame by said rod, which, conversely, transmits the stress on the frame to the axle, the effectiveness of the above steering assembly is reduced over rough ground, in which case handling the tractor is particularly strenuous and may result in the driver becoming distracted through fatigue.
Accordingly, it would be desirable to provide an improved steering mechanism that can be utilized on agricultural tractors.